Selective and sensitive detection of nitrite based on NO sensing on a polymer-coated rotating disc electrode

A new effective way of nitrite detection in complex samples is presented. It is based on chemical conversion of nitrite to nitric monoxide (NO) in acidic aqueous solution containing hexacyanoferrate(II) as a reductor. NO is then detected on a poly-eugenol coated platinum electrode. When the electrode is rotating and the reduction medium is continuously purged with nitrogen, the addition of a nitrite-containing sample produces narrowed current spikes. The peak current is proportional to nitrite content in the sample over the range of 5.0–100 μM and detection limit is 0.6 μM. The method is simple and highly reproducible. Relative standard deviation of 10 repetitions is less than 4%. Practical utility of the proposed approach is demonstrated by nitrite determination in human saliva.     

Complexes of tetra-tert-butyl-tetraazaporphine with Al(III) and Zr(IV) cations as fluoride selective ionophores

In this work, complexes of Zr(IV) and Al(III) cations with 2,7,12,17-tetra-tert-butyl-5,10,15,20-tetraazaporphine (TAP) were tested as ionophores in plasticized PVC membranes of ion-selective electrodes. It was found that both tested ionophores show enhanced affinity towards fluoride anion. High fluoride selectivity was observed in the presence of anionic or cationic additives in the membrane, which indicates that proposed compounds work according to charged or neutral carrier mechanism, depending on membrane composition and pretreatment.tert-Butyl substituents, present in the structure of tested compounds, were supposed to prevent formation of ionophore dimers within the membrane phase. This process was found to be responsible for some unfavorable potentiometric properties of electrodes based on complexes of Zr(IV) and Al(III) cations with porphyrins (compounds closely related to tetra-tert-butyl-5,10,15,20-tetraazaporphine). As it was shown using spectrophotometrical measurements, Al(III)-TAP was not susceptible to dimerization, while dimer formation was observed for Zr(IV)-TAP. In full agreement with these observations, electrodes with membranes containing Al(III)-TAP responded in near-Nernstian and fast manner towards fluoride anion, while the employment of Zr(IV)-TAP as ionophore resulted in super-Nernstian and sluggish response. Plasticized PVC membranes doped with Al(III)-TAP and 20 mol% of lipophilic anionic additives shown remarkable F⁻ selectivity, with selectivity coefficients, , as follows: −4.4 (Y⁻Br⁻), −4.3 (Cl⁻), −4.2 (NO₃⁻), −3.6 (SCN⁻), −2.9 (ClO₄⁻).     

Zirconium(IV)-porphyrins as novel ionophores for fluoride-selective polymeric membrane electrodes

The feasibility of using Zr(IV)-porphyrins as novel ionophores for preparing anion-selective polymeric membrane electrodes is examined. Electrodes constructed using o-nitrophenyl octyl ether plasticized poly(vinyl chloride) membranes containing Zr(IV)-octaethylporphyrin (OEP) dichloride (Zr(IV)[OEP]Cl₂) or Zr(IV)-tetraphenylporphyrin (TPP) dichloride (Zr(IV)[TPP]Cl₂) were found to exhibit enhanced potentiometric selectivity toward fluoride compared to electrodes based on a typical anion-exchanger (e.g. tridodecylmethylammonium chloride). At pH 5.5, the electrodes displayed the following selectivity sequences: ClO₄⁻ > SCN⁻ > I⁻ > F⁻ > NO₃⁻ > Br⁻ > NO₂⁻ > Cl⁻ and F⁻ > ClO₄⁻ > SCN⁻ > I⁻ > NO₂⁻ > NO₃⁻ > Br⁻ > Cl⁻ for membranes doped with Zr(IV)[OEP]Cl₂) and Zr(IV)[TPP]Cl₂, respectively. Both ionophores are shown to operate via a charged carrier mechanism, with 10 mol% of lipophilic tetraphenylborate derivative in the membrane phase required to achieve optimal selectivity. Electrodes prepared with both metalloporphyrin species display super-Nernstian response toward fluoride with slopes typically greater than −100 mV per decade. It is shown, via UV-VIS spectroscopy of the membrane phase, that this behavior occurs due to spontaneous formation of hydroxide ion bridged porphyrin dimers in the membrane in the presence of the lipophilic anionic additive. The dimers are easily converted to monomeric species upon increasing the concentration of fluoride in the sample solution. Decreasing the pH of sample buffer background solution (from pH 5.5 to pH 3) decreases the lower detection limit (DL) of the electrode response toward fluoride (by two-order of magnitude) and improves the electrodes’ selectivity.     

脂溶性酞菁钴(III)为载体的高选择性亚硝酸根PVC膜电极

以自制的4,4',4',4''-四特丁基酞菁钴(II)为原料合成二氯4,4',4',4''-四特丁基酞菁钴(III)。以此为载体制备PVC膜电极。该电极的电位选择性次序明显不同于Hofmeister次序, 其最佳 响应斜率为-52mV/pNO2^-, 线性范围为3×10^-^5～1×10^-^1mol.dm^-^3NaNO2。通过改变配合物轴向的配位阴离子, 用紫外-可见光谱法对电极的响应机理作了初步探讨。     

Development of a selective optical sensor for Cr(VI) monitoring in polluted waters

An optical sensor is described for the sensitive and selective determination of the Cr(VI) ion in aqueous solutions. The optode membrane is prepared by incorporating Aliquat 336 as an ionophore and a chromoionophore (4',5'-dibromofluorescein octadecyl ester) in a poly(vinyl chloride) (PVC) membrane containing ortho-nitrophenyloctyl ether (o-NPOE) as a plasticizer. The response to Cr(VI) is indicated by co-extraction of the target species and of hydrogen ions into the bulk of the membrane yielding large absorbance changes which can easily be measured in the visible spectral range. The optode membrane shows a reversible response in the concentration range of 1.1x10(-5)-1.0x10(-3) M and has been shown to be more selective towards the HCrO4(-) ion than other anions with a selectivity pattern HCrO4(-) > SCN- approximately = ClO4(-) > NO3(-) approximately = I- approximately = NO2(-) > H2PO4(-) approximately = Cl- approximately = SO4(2-). The sensing method developed has successfully been applied to the determination of Cr(VI) in spiked river water as well as in electroplating rinse waters.     

Chromium(III) selective membrane sensors based on Schiff bases as chelating ionophores

The two chromium chelates of Schiff bases, N-(acetoacetanilide)-1,2-diaminoethane (L₁) and N,N′-bis(acetoacetanilide)-triethylenetetraammine (L₂), have been synthesized and explored as neutral ionophores for preparing poly(vinylchloride) (PVC) based membrane sensors selective to Cr(III). The addition of lipophilic anion excluder (NaTPB) and various plasticizers viz. o-Nitrophenyloctyl ether (o-NPOE), dioctylpthalate (DOP), dibutylphthalate (DBP), tris(2-ethylhexyl)phosphate (TEHP), and benzyl acetate (BA) have found to improve the performance of the sensors. The best performance was obtained for the membrane sensor having a composition of L₁:PVC:DBP:NaTPB in the ratio 5:150:250:3 (w/w). The sensor exhibits Nernstian response in the concentration range 8.9 × 10⁻⁸ to 1.0 × 10⁻¹ M Cr³⁺ with limit of detection 5.6 × 10⁻⁸ M. The proposed sensor manifest advantages of relatively fast response (10 s) and good selectivity over some alkali, alkaline earth, transition and heavy metal ions. The selectivity behavior of the proposed electrode revealed a considerable improvement as compared to the best previously PVC-membrane electrode for chromium(III) ion. The potentiometric response of the proposed sensor was independent of pH of the test solution in the range of 2.0-7.0. The sensor has found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol and acetonitrile and could be used for a period of 3 months. The proposed electrode was used as an indicator electrode in potentiometric titration of chromium ion with EDTA and in direct determination in different water and food samples.     

Capacitive sensors using electropolymerized o-phenylenediamine film doped with ion-pair complex as selective elements for the determination of pentoxyverine

A capacitive sensing method based on electropolymerized o-phenylenediamine film doped with pentoxyverine ion-pair complex as selective element was successfully developed for the determination of pentoxyverine. Ion-pair complex, pentoxyverine-tetraphenylborate or pentoxyverine-picrolonate, was embedded in electropolymerized o-phenylenediamine film by electropolymerizing technique. The effects of working frequency and test solution pH on the detection of pentoxyverine were investigated in detail and optimized. For the sensor modified with pentoxyverine-tetraphenylborate, calibration curve was linear over the concentration range of 5.0×10⁻⁷ to 1.0×10⁻⁴ M with a detection limit of 1.0×10⁻⁷ M at pH 7. The proposed sensor exhibited high selectivity and sensitivity to pentoxyverine. The results in sample analysis confirmed the usefulness of the proposed ISC sensor for quantitative analysis, and also indicated that this method might find applications in the assay of other drugs.     

Comparative study on 2-amino-1,4-naphthoquinone derived ligands as indium (III) selective PVC-based sensors

The three different ligands (Q₂ to Q₄) based on 2-amino-1,4-naphthoquinone (Q₁), have been synthesized and explored as neutral ionophores for preparing polyvinyl chloride-based membrane sensors selective to indium (III). The addition of potassium tetrakis(4-chlorophenyl) borate and various plasticizers, viz., o-NPOE, DBP, DBBP, DOP and CN has been found to substantially improve the performance of the sensors. The best performance was obtained with the sensor no. 16 having membrane of ligand (Q₂) with composition (%, w/w) ionophore Q₂ (3.0%):PVC (30.0%):o-NPOE (63.0%):KTpClPB (4.0%). This sensor exhibits Nernstian response with slope 19.8 mV/decade of activity in the concentration range 2.5 × 10⁻⁷ to 1.0 × 10⁻² M indium (III), performs satisfactorily over wide pH range of (2.5-7.5) with a fast response time (10 s). The sensor was also found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of acetonitrile, ethanol and methanol. The proposed sensor can be used over a period of 3.5 months without significant drift in potentials. The quantitative application of sensor was also evaluated by comparative analysis of artificially made sea water with AAS.     

Amperometric sensor for nitrite using a glassy carbon electrode modified with alternating layers of iron(III) tetra-(N-methyl-4-pyridyl)-porphyrin and cobalt(II) tetrasulfonated phthalocyanine

The development of a highly sensitive amperometric sensor for nitrite using a glassy carbon electrode modified with alternated layers of iron(III) tetra-(N-methyl-4-pyridyl)-porphyrin (FeT4MPyP) and cobalt(II) tetrasulfonated phthalocyanine (CoTSPc) is described. The modified electrode showed an excellent catalytic activity and stability for the nitrite oxidation decreasing the peak potentials about 200 mV toward less positive values and presenting much higher peak currents than those obtained on the bare GC electrode. A linear response range of 0.2-8.6 μmol l⁻¹, with a sensitivity of 0.37 μA l μmol⁻¹ and detection limit of 0.04 μmol l⁻¹ were obtained with this sensor. The repeatability of the proposed sensor, evaluated in term of relative standard deviation, was verified to be 1.4% for 10 measurements of 0.2 μmol l⁻¹ nitrite solution. Interference caused by common ions has been investigated in simulated mixtures containing high concentration level of interfering ions and the sensor was found to be tolerant against these ions. The developed sensor was applied for the nitrite determination in water samples and the results were in agreement with those obtained by a comparative method described in the literature. The average recovery for these samples was 100.1 (±0.7)%.     

Polymethacrylate polymers with appended aluminum(III)-tetraphenylporphyrins: Synthesis, characterization and evaluation as macromolecular ionophores for electrochemical and optical fluoride sensors

The synthesis and characterization of a novel polymethacylate polymer with covalently linked Al(III)-tetraphenylporphyrin (Al(III)-TPP) groups is reported. The new polymer is examined as a potential macromolecular ionophore for the preparation of polymeric membrane-based potentiometric and optical fluoride selective sensors. To prepare the polymer, an Al(III) porphyrin monomer modified with a methacrylate functionality is synthesized, allowing insertion into a polymethacrylate block copolymer (methyl methacrylate and decyl methacrylate) backbone. The resulting polymer can then be incorporated, along with appropriate additives, into conventional plasticized poly(vinyl chloride) films for testing electrochemical and optical fluoride response properties. The covalent attachment of the Al(III)-TPP ionophore to the copolymer matrix provides potentiometric sensors that exhibit significant selectivity for fluoride ion with extended lifetimes (compared to ion-selective membrane electrodes formulated with conventional free Al(III)-TPP structure). However, quite surprisingly, the attachment of the ionophore to the polymer does not eliminate the interaction of Al(III)-TPP structures to form dimeric species within the membrane phase in the presence of fluoride ion. Such interactions are confirmed by UV/visible spectroscopy of the blended polymeric films. Use of the new polymer-Al(III)-TPP conjugates to prepare optical fluoride sensors by co-incorporating a lipophilic pH indicator (4′,5′-dibromofluorescein octadecyl ester; ETH7075) is also examined and the resulting optical sensing films are shown to exhibit excellent selectivity for fluoride, with the potential for prolonged operational lifetime.     

Poly(norbornene)s as matrix materials for platinum tetrakis(pentafluorophenyl)porphyrin based optical oxygen sensors

A set of poly(norbornenes) was prepared using ring opening metathesis polymerization (ROMP) and used as matrix material for the preparation of optical oxygen sensor layers based on platinum tetrakis(pentafluorophenyl)porphyrin (PtTFPP) as the sensitive dye. Different polymers were prepared and investigated in order to retrieve information on the influence of the anchor group and the side chain attached to the polymer backbone on their performance as matrix material for the dye. Bulky side groups increased the oxygen permeability through ROM polymer layers, especially when the bulky group was directly attached via an anchor group to the polymer backbone without any aliphatic spacer in between. Sensor layers made of poly(endo,exo[2.2.1]bicyclo-5-heptene-2,3-dicarboxyclic acid di-tert-butylester) and PtTFPP exhibited the highest τ₀/τ ratio and responded strongly to small amounts of oxygen.     

Study of Cobalt(III) Corrole as the Neutral Ionophore for Nitrite and Nitrate Detection via Polymeric Membrane Electrodes

Cobalt(III) 5,10,15‐tris(4‐tert‐butylphenyl) corrole was synthesized and incorporated into plasticized poly(vinyl chloride) membranes and studied as a neutral carrier ionophore via potentiometry. This cobalt(III) complex has binding affinity to nitrite, and the resulting membrane electrode yields reversible and Nernstian response toward nitrite. Enhanced nitrite selectivity is observed over other anions, including lipophilic anions such as thiocyanate and perchlorate when an appropriate amount of lipophilic cationic sites are added to the membrane phase. Detection limit to nitrite is ca. 5 µM. Using tributylphosphate as the plasticizer with the cobalt(III) corrole species yields electrodes with enhanced nitrate selectivity.     

A sensitive and selective fluorescence sensor for the detection of arsenic(III) in organic media

Arsenic contamination is a leading environmental problem. As such, levels of this toxic metalloid must be constantly monitored by reliable and low-cost methodologies. Because the currently accepted upper limit for arsenic in water is 10 ppb, very sensitive and selective detection strategies must be developed. Herein we describe the synthesis and characterization of a fluorescent chemical probe, namely, ArsenoFluor1, which is the first example of a chemosensor for As(3+) detection in organic solvents at 298 K. AF1 exhibits a 25-fold fluorescence increase in the presence of As(3+) at λ(em) = 496 nm in THF, which is selective for As(3+) over other biologically relevant ions (such as Na(+), Mg(2+), Fe(2+), and Zn(2+)) and displays a sub-ppb detection limit.     

Simple, sensitive and selective detection of dopamine using dithiobis(succinimidylpropionate)-modified gold nanoparticles as colorimetric probes

In this paper, we report a simple, sensitive and selective colorimetric visualization of dopamine (DA) using dithiobis(succinimidylpropionate) (DSP)-modified gold nanoparticles (AuNPs) as probes and ferric ions as cross-linkers. Via the standard amine coupling reaction between the amino groups of DA and activated carboxyl groups of DSP, DA molecules can be assembled onto the surface of DSP-AuNPs. Accordingly, Fe(3+) ions induce a change of DSP-AuNPs in color and UV-vis absorbance by coordinating to the catechol groups of the anchored DA. The pH dependence and mechanism of this method are discussed. A detection limit of 2 nM was obtained, which is lower than those achievable with currently used chromatographic and electrochemical techniques. The feasibility for the detection of DA in artificial cerebrospinal fluid has been demonstrated.     

Highly sensitive and selective amperometric sensors for nanomolar detection of iodate and periodate based on glassy carbon electrode modified with iridium oxide nanoparticles

Iridium oxide nanoparticles are grown on a glassy carbon electrode by electrodepositing method. The electrochemical behavior and electrocatalytic activity of modified electrode towards reduction of iodate and periodate are studied. The reductions of both ions occur at the unusual positive peak potential of 0.7 V vs. reference electrode. The modified electrode is employed successfully for iodate and periodates detection using cyclic voltammetry, hydrodynamic amperometry and flow injection analysis (FIA). In the performed experiments, flow injection amperometric determination of iodate and periodate yielded calibration curves with the following characteristics: linear dynamic range up to 100 and 80 μM, sensitivity of 140.9 and 150.6 nA μM⁻¹ and detection limits of 5 and 36 nM, respectively. The repeatability of the modified electrode for 21 injections of 1.5 μM of iodate solution is 1.5%. The interference effects of NO₂⁻, NO₃⁻, ClO₃⁻, BrO₃⁻, ClO₄⁻, SO₄²⁻, Cu²⁺, Zn²⁺, Mn²⁺, Mg²⁺, Cd²⁺, Ca²⁺, Na⁺, K⁺, NH₄⁺ and K⁺, CH₃COO⁻ and glucose were negligible at the concentration ratio of more than 1000. The obtained attractive analytical performance together with high selectivity and simplicity of the proposed method provide an effective and e novel modified electrode to develop an iodate and periodate sensor. Sensitivity, selectivity, the liner concentration range and the detection limit of the developed sensor are all much better than all known similar sensors in the literature for iodate and periodate determination.     

Highly sensitive and selective detection of silver(I) ion using nano-C60 as an effective fluorescent sensing platform

In this Communication, we report water-soluble nano-C(60) in the first use as an effective fluorescent sensing platform for the highly sensitive and selective detection of Ag(+). The general concept used in this approach is based on a fluorescently labeled single-stranded DNA (ssDNA) probe that adsorbs on nano-C(60), leading to substantial dye fluorescence quenching; however, in the presence of Ag(+), C-Ag(+)-C coordination induces the probe to fold into a hairpin structure, which does not adsorb on nano-C(60) and thus retains the dye fluorescence. This sensing system exhibits a detection limit as low as 1 nM and has a high selectivity against other metal ions. Finally and most importantly, we demonstrate its performance in real sample analysis.     

A distyryl BODIPY derivative as a fluorescent probe for selective detection of chromium(III)

A new boradiazaindacene (BODIPY) derivative (1a) bearing simple NO bidentate ligands has been synthesized. The 1a molecule behaves as a fluorescent probe for Cr³⁺ and shows strong red fluorescence upon coordination with Cr³⁺, while showing almost no fluorescence for other metal cations.     

Nitrogen and sulfur co-doped carbon quantum dots for highly selective and sensitive fluorescent detection of Fe(III) ions and L-cysteine

Microchimica Acta - Nitrogen and sulfur co-doped carbon quantum dots (N,S-CQDs) with a high quantum yield (69%) and excellent photoluminescent properties were synthesized via a facile hydrothermal...     

A rapid, selective and sensitive spectrophotometric method for the determination of Ce(III) using some bisazophenyl-beta-diketone derivatives

A rapid, simple, selective and sensitive spectrophotometric method for the determination of cerium(III) using the title azo dyes [1,3-phenylenediamine bisazoacetylacetone (I(a));1,3-phenylenediamine bisazobenzoylacetone (I(b));1,4-phenylenediamine bisazoacetylacetone (I(c)); and 1,4-phenylenediamine bisazobenzoylacetone (I(d))] has been developed in neutral and slightly alkaline (pH 7.00, 7.50, 8.00 and 7.00) media. The 1:1 and 2:1 (M:L) complexes formed exhibit their highest absorbances in 30% (v/v) dioxane solutions, having formation constants (log K) of 4.44, 4.95. 5.63 and 5.22 and 8.51, 8.76, 9.73 and 9.37 respectively. Beer's law is obeyed over the concentration ranges 0.10-2.50, 0.05-3.00, 0.05-3.75 and 0.10-3.50 mug ml(-1) of cerium(III). More accurately, Ringbom optimum concentration ranges are 0.2-2.25, 0.2-2.6, 0.2-3.5 and 0.2-3.3 mug ml(-1) for the complexes of reagents I(a),I(b),I(c) and I(d) respectively. The molar absorptivities, Sandell sensitivities and relative standard deviations were also calculated. The interferences of 50 foreign ions on the determination of cerium(III) were studied. The method allows the determination of cerium(IV) after prior reduction to the trivalent state. The proposed method was used for cerium determination in two different monazite samples and the results were compared with certified values obtained using atomic absorption spectrometry, indicating that the procedure provided accurate and precise results.